This invention relates generally to semiconductor photolithograph and, in particular, to applying sub-resolution assist features.
Various systems may be used to print features, such as patterns, that define integrated circuits on semiconductor wafers. In general, electromagnetic wave emissions from a source are directed to expose selected locations on a substrate, while leaving other locations unexposed. Examples of emissions include visible light, ultraviolet (UV), and extreme ultraviolet (EUV) radiation, and x-rays. These emissions all have characteristic wavelengths in various media.
Example approaches to directing these emissions towards selected locations include selective attenuation (e.g., using binary photomasks), interference (e.g., using phase shifting masks), reflection (e.g., using EUV reflective optical elements), and beam steering. Regardless of the approach used, systems for printing features have a resolution limit below which certain features are not resolved during printing. In particular, it is desirable to manufacture features that are smaller than the lithographic wavelength. However, attempting to form features at these sizes, while achieving adequate resolution, may be complex. As mask features get closer together, a number of issues may arise, including diffraction issues.